1. Technical Field
This invention relates to improvements in an electrode for electric discharge surface treatment and a manufacturing method thereof used in electric discharge surface treatment operations for forming a hard coating made of an electrode material on the surface of a treated material or a hard coating made of a substance in which the electrode material reacts by electric discharge energy through the energy by generating electric discharge between the electrode and the treated material.
2. Background Art
Conventionally, as a technique of forming a hard coating on the surface of a treated material to provide corrosion resistance or abrasion resistance, there is an electric discharge surface treatment method disclosed in, for example, JP-A-5-148615. This technique is an electric discharge surface treatment method of a metal material comprising two steps of performing primary processing (deposition processing) using a green compact electrode obtained by mixing a WC (tungsten carbide) powder and a Co (cobalt) powder to perform compression molding and then performing secondary processing (remelting processing) by replacing the green compact electrode with an electrode with relatively small electrode consumption such as a copper electrode. In this method, a hard coating having strong adhesion strength to a steel material can be formed, but it is difficult to form a hard coating having strong adhesion strength to a sinter material such as cemented carbide. However, according to our research, it has been found that when a material for forming hard carbide such as Ti (titanium) is used as an electrode and electric discharge is generated between the electrode and a metal material which is a treated material, a strong hard coating can be formed on the surface of the metal which is the treated material without a process of remelting. This is because carbon which is a component in processing liquid reacts with the electrode material consumed by the electric discharge to form TiC (titanium carbide). Also, it has been found that when by a green compact electrode of metal hydride such as TiH2 (titanium hydride), electric discharge is generated between the electrode and a metal material which is a treated material, a hard coating with the adhesion higher than that of the case of using a material such as Ti can speedily be formed. Further, it has been found that when by a green compact electrode in which other metals or ceramics are mixed with the hydride such as TiH2, electric discharge is generated between the electrode and a metal material which is a treated material, a hard coating with various properties such as hardness or abrasion resistance can speedily be formed. Such a method is disclosed in, for example, JP-A-9-192937, and a configuration example of an apparatus used in such electric discharge surface treatment will be described by way of FIG. 3. In the drawing, numeral 1 is a green compact electrode obtained by compressedly molding a TiH2 powder, and numeral 2 is a treated material, and numeral 3 is a processing bath, and numeral 4 is a processing liquid, and numeral 5 is a switching element for performing switching of voltage and current applied to the green compact electrode 1 and the treated material 2, and numeral 6 is a control circuit for performing on-off control of the switching element 5, and numeral 7 is a power source, and numeral 8 is a resistor, and numeral 9 is a hard coating formed. By such a configuration, the hard coating 9 having strong adhesion strength can be formed on the surface of the treated material 2 such as steel or cemented carbide through electric discharge energy by generating electric discharge between the green compact electrode 1 and the treated material 2.
There is a problem in that an electrode used in such electric discharge surface treatment is difficult to handle unless the electrode has a certain degree of strength and also the electrode crumbles excessively by electric discharge energy at the time of the electric discharge surface treatment and the electrode material cannot adhere to the surface of the treated material in a state of melting. Also, in case that the strength of the electrode is high and the electrode hardens excessively, there is a problem in that the electrode is difficult to crumble by electric discharge energy at the time of the electric discharge surface treatment and processing efficiency reduces. Thus, the electrode for electric discharge surface treatment requires moderate strength and crumbliness. As a material having such properties, metal hydride is given, but since there is danger of spontaneous combustion in case that the metal hydride touches at water, there is a problem in a safety standpoint. Therefore, a practical electrode for electric discharge surface treatment including the metal hydride in the electrode material cannot be obtained.